4-Aminodiphenylamine is an important intermediate of antioxidant and stabilizer and an important chemical product for rubber industry and polymer industry. 4-aminodiphenylamine can be reductively alkylated by the well known methods to make alkylated p-phenylenediamines. Depending on the starting materials, known methods for preparing 4-aminodiphenylamine include:
(1) aniline method, where p-nitro-chlorobenzene and aniline as raw materials react in the presence of a catalyst to produce 4-nitrodiphenylamine, then, 4-nitrodiphenylamine is reduced by sodium sulfide to form 4-aminodiphenylamine;
(2) formanilide method, where formic acid and aniline are used as starting materials to prepare formanilide, which in turn reacts with p-nitro-chlorobenzene in the presence of an acid-binding agent such as potassium carbonate, to produce 4-nitrodiphenylamine, and then, 4-nitrodiphenylamine is reduced by sodium sulfide to form 4-aminodiphenylamine;
(3) diphenylamine method, where diphenylamine as raw material is nitrosated using a nitrite in an organic solvent to produce N-nitrosodiphenylamine, which is rearranged to 4-nitrosodiphenylamine hydrochloride under the action of anhydrous hydrogen chloride, and then, 4-nitrosodiphenylamine hydrochloride is neutralized with a base to give 4-nitrosodiphenylamine which is finally reduced to 4-aminodiphenylamine by sodium sulfide.
Although these methods use different starting materials, sodium sulfide is usually used as the reducing agent to prepare 4-aminodiphenylamine. These reactions suffer from severe reaction conditions, complex operation, high energy consumption, low yield, high cost, and environment pollution caused by concomitant waste water, waste gas, and waste residues.
Among the preparation methods for 4-aminodiphenylamine, some methods use nitrobenzene, nitrobenzene and aniline, or nitrosobenzene as raw materials to carry out condensation reaction, and then use hydrogen gas to perform hydrogenation to produce 4-aminodiphenylamine. In fact, it was reported in 1901 (Wohl, Chemische Berichte 34, p. 2442 (1901)) and 1903 (Wohl, Chemische Berichte 36, p. 4135 (1903)) that nitrobenzene reacted with aniline under the action of a base to form 4-nitrosodiphenylamine and 4-nitrodiphenylamine. However, the method had been neither regarded as important nor developed because of the relative low yield until 1990s when it was researched and developed again and achieved some progress. See DE 19734055.5, DE 19810929.6, and DE 19709124.5. However, the methods as disclosed in the art have disadvantages.
First, the catalysts used in these methods are expensive, which results in relatively high production cost in an industrial-scale production. Thus, these methods have no advantage over other conventional methods. For examples, tetraalkyl ammonium hydroxide and fluoride used in condensation reaction and noble metal, such as palladium, platinum, rhodium, and the like, used in hydrogenation reaction are expensive. The instability of tetraalkyl ammonium hydroxide imparts some difficulty to the recovery and reuse of tetraalkyl ammonium hydroxide. In addition, the use of noble metal hydrogenation catalysts applies higher requirements to raw materials and equipment. Second, the yield is relatively low, which makes the methods only suitable for laboratory research. This is why these methods have been difficult to be industrially applied. Third, the operation is complicated. These methods are not in favor of continuous operations, which limits the production scale. Fourth, separation is difficult and purity of product is not high.
U.S. Pat. No. 6,395,933 discloses a process for synthesizing 4-aminodiphenylamine by reacting nitrobenzene and a substituted aniline at a certain temperature in the presence of a strong base and a phase-transfer catalyst. The process is not satisfactory in yields, and there are many side reactions. In the product mixture of 4-nitrodiphenylamine and 4-nitrosodiphenylamine, the proportion of 4-nitrodiphenylamine is too high which indicates that too much hydrogen has been consumed during the hydrogenation reaction and the production cost is thereby significantly increased. Furthermore, the process needs an oxidizing agent, which makes it unsuitable for industrial production.
WO 93/00324 discloses a process for preparing 4-aminodiphenylamine by reacting nitrobenzene and aniline at a proper temperature in a proper solvent in the presence of a base with the contents of proton materials in solution being controlled. The process requires a solvent and the control of the contents of proton materials in the solution. The introduction of the solvent results in increased energy consumption and difficulty for separation. Controlling the contents of proton materials gives rise to difficulty for operation and control of the reaction. In particular, at a later stage of the condensation reaction, controlling the contents of proton materials, which mainly means dehydration to lower water content, prolongs the reaction time and causes partial aniline to be entrained out. The later stage, the more difficult removing the proton materials. Controlling the proton materials at a certain range is difficult, and goes against industrial production. The expensive tetraalkyl quaternary amine base catalyst will quickly decompose in the course of controlling the contents of proton materials to a range of from 0.5 to 4 percent, resulting in increased production cost.